Corrosion inhibition



Aug. 1'9, 1952 P. sQvlLEs CoRRosIoN INHIBITIONl Filed July 18, 1949 OOw 3 'aA/Nl Noiivuiana ivy/mis mvENToR.

AGENT.

Patented Aug. 19, 1952 CORROSION INHIBITION Prentiss S'. Viles, Baytown, Tex., assignor, by 'mesne assignments, to Standard Oil Development Company, Elizabeth, N. J., a corporation of Delaware Application July 18, 1949, Serial No. 105,326 Y 3 Claims. 1

anda method for preparing the composition. In

itsV more particular aspects, the invention is directed to a new chromium salt, a method of preparing same and the employment of the composition in inhibiting the corrosivity of corrosive solutions to ferrous metal surfaces.

Prior, to the present invention it has been known to employ alkali metal chromium salts as corrosion inhibitors to inhibit the corrosivity of oxygen bearing water. It has also been known to inject alkali' metal salts of chromium into wells producing corrosive fluids from subsurface formations. For example, it has been known to use potassium and sodium chromate as corrosion inhibitors in oxygen bearing Water and also as corrosion inhibitors in wells producing gas and liquidfrom subsurface formations such as oil and gas wells. It has been common heretofore to introduce the potassium and sodium chromates into water or into well fluids and the like to inhibit the corrosivity of the corrosive fluids against ferrous metal surfaces such as vessels'and metal conduits with Vwhich they come into contact. OxygenV is known to be present in waterV used in industrialgprocesses suchas petroleum refining and such water is quite corrosive to ferrous metal surfaces with which it comes intoi contact such as in condenser boxes and the like. The corrosive mediain well fluids such as those in the type referred to is usually hydrogen sulde or carbon dioxide, which may be produced in substantial quantities'depending on the locale of the Well.

It has also been known to employ various amines such as cyclohexylamineas corrosion inhibitors in steam systems. Berk, in the U. S. Bureau of Mines publication Observations'on the Use of Cyclohexylamine inv Steam, discusses the use of amines andv particularly cyclohexylamine as a corrosion inhibitor in systems where corrosion is due to theA presence of Icarbon dioxide. Chamberlain has disclosed in U. S. 1,719,649 and U. S. 1,719,650, the employment of amines ascorrosion inhibitorsin acidic solutions. Other patentees such as Hitch in U. S. 1,206,220, Gann et al. in U. S. 1,992,205 and Saukaitis in U. S. 2,049,517 have disclosed the inhibiting action of sodium and 'potassium"chromates, sodium bichromate and the; inhibiting power of various amines in vinhibiting the corrosivity of acidic media to various alloys. Thus from the foregoing discussion of the priorart it will be seen that it 2 is old to employ amines or-chromates as corrosion inhibitors.

The corrosion inhibitors of the prior art, either amines or'chromates. have the one great disadvantage in requiring appreciable amounts of the inhibitors to passivate the corrosivity of various solutions to which they may be added. In other words, substantial quantities of the compounds of the prior art have been necessary. These corrosion inhibitors are quite costly and besides, in industrial systems, add other `ingredients to the corrosive solution which may be disadvantageous.

It is, therefore, the main object of the present invention to provide an improved composition adapted for use as a corrosion inhibitor of corrosion to ferrous metals due to aqueous solutions containing oxygen, hydrogen sulfide and carbon dioxide.

Another object of the present invention is to provide a method for preparing a composition adapted for use as a corrosion inhibitor in corrosive aqueous solutions containing oxygen, hydrogen sulfide or carbon dioxide in contact with ferrous metal surfaces. Y

It is another object of Vthe-presentlinvention to provide an improved method for inhibiting the corrosivity of aqueous solutions in contact with ferrous metal surfaces.

A still further object of the present invention is to provide a method for inhibiting the corrosivity of aqueous solutions containing. corrosive amounts of oxygen, hydrogen sulfide and carbondioxide in contact with a ferrous metal surface. Y Y

The objects of the present invention may be achieved by preparingv a composition adapted to be used as a corrosion inhibitor, as described, by reacting a solution of an acidic chromium compound and an amine.

The objectsof the present invention may also be achieved by maintainingin the corrosive solution in contact with ferrous metal surfaces containing oxygen, hydrogen sulfide or carbon dioxide, a small but effective amount of the reaction product of an acidic chromium compound and an amine. f

Thusthe-present invention may be brieiiy described as involving acomposition comprising a reaction product of an acidic chromium compound and an amine. Y

The invention also :involves preparing a composition by forming an aqueous solution of an acidic chromium compound such as the chromic acids, salts of polychromic acids, and acid chromium salts and adding to the aqueous solution gen, hydrogen sulfide, and/or carbon dioxide inV contact with the ferrous metal surface a small K solution.

ployed, satisfactory results have been obtained With solutions of potassium dichrcmate containing by Weight of the salt. The amount of the amine employed should be suicient to proe vide at least two moles of amine for each mole of the acid chromium compound in the aqueous In general, one mole of amine will react with i every mole of acid chromate present originally but effective amount of the reaction'lproduct of an amine and an acidic chromium compound, such as the chromic acids, the salts of. polychromic acids and acid chromium` salts inthe range between 5 and 500 parts permillion of the corrosive solution. f

The term acidic chromium compound, refers t0 those compounds which when placed in aqueous solution will have a pH less than 7. amples of such salts are potassium dichromate, sodium acid chromate, potassium .trichromata and sodium trichromate. It is toA be noted that an alkali metal chromate such as potassium chromate` or sodium chromate will not react with amines in accordance! with .this invention since they form solutions wi-th a pH greater than 7. It is well known, however, that in acid solution the chromatestend to form polychromates, the concentration of which depends upon the pH of thesolution and the concentration of the salt. These polychromates will react with amines in accordance with the present invention as describedlhereinafter; f l

In preparing the-improved composition, an acidic chromium compound of Ythe typeillustrated such vas an alkali metal dichromate, is dissolved in water tothe extent of forming a solutionvwhich is only partially saturated. vIt is desirable to employ the highest practical degree of concentration of the acidic chromium compound solution, but careshould be exercised in preparingV the solution since, if the solution is too concentrated, it may cause oxidation to occur as Will bedescribed. yA primary, secondary, or tertiary amine is then `added to the aqueous solution of the'- acidic chromium salt. If the aqueous solution Vcontainstoo much of the acidic chromium compoundA there` is some danger of oxidation of the amineV bythe solution. The degree of saturation maybe determined by the skilled Workman; The amine isreacted with the aqueoussolution of the chromium compound acid chromiumsalt until a pronounced color change takes place. With potassium dichromate the aqueous rsolution is'A a brilliant orange which on reaction with an amine changes to an intense yellow. When the reaction hasI beencompleted, as indicated by the Vcolor change, the reaction product has been formed which is suitable as a corrosion inhibitor and maybe used as such as a solution or the reaction product ma-y be recovered from the solution by evaporation of the solution to drynessto Cause separation of the crystalline satis.

The temperatures employed are essentially room temperatures, that is, a temperature in the range from about 60 to 100 E. While the reaction is taking place some heat will be evolved as normally occurs in acid-alkaliV reactions. However, elevated temperatures should be. avoided since oxidation rof the amine by theacid chromium compound may occur. Itis undesirable to use temperatures in excess of about 212 F.

While solutions of greater strength may boem- 4or formed in solution. For example, a mole of potassium dichromate, which hydrolyzes to form two moles of the acid chromate, requires two ,moles of'amine .to form the reaction product of deep orangeoolorgyas titrated with cyclohexylamine until the color changed to yellow. This `color change, which was quite pronounced, oc-

curred when 39 cc. of the cyclohexylamine had been added. The 50 grams of potassium dichromate corresponds to 0.17v mole whereas the 39 cc. of cyclchexyla'mine corresponds to 0.32 mole. Thus, Within the limits of experimental error, 2 moles ofthe amine were required for one mole of the dichromate. Since any of the salts of the polychromatic acids hydrolyze to form the acid chromate, they may be used to form the amine chromates. Forthe trchromate, 3 moles of the amine would be required, for the tetrachromate, 4 moles of the amine would be required, etc.

ItV has been stated that the chromium compound'to be used with the; .present invention must form an aqueousfsolution with a pH less than '7. Any of the compounds illustrated, such as the chromicV acids', salts. ofpollychromicv acids, or acid chromium salts, meet this criterion. Alkali metal chromates. onthe other hand form solutions whose pH is 'greater than '7 and, thus, Will not react in accordance Awiththe present invention.. This `risfillustrated by the following example:v 20. grams. of sodium chromate were addedto 200 cc. of'distillecl water and the pI-I was found to be 9. 'IWo drops of' cyclohexylamine were added to.v this solution whereupon the pH immediately rose to a value of slightly greater than. 11, thus indicating that thecyclohexylamine wasn'ot reacting with the chromato. For thepurpose'of: comparison, three drops of cyclohexylamine were addedv to- 200 milliliters of distille'd water and the pHv was found tobe 1v1.

Itis Well known that the chromates, ifplaced in a4 strong enough acid. solution, tend to form the. polychromates. The concentration ofl the polychromates formed depends upon the pH of the solution and the concentration of the chromate originally present.` '-IIiepolychromates y formed in such a mannerrwi-lli react with amines in accordance with4 the present invention. For convenience, however', itv ifsy preferred touse either the chromic acids or the salts-of'thepolychromic acids, orA an acid chromium salt. since solutions of these compounds. do not have to` beradjusted for pI-I in order to obtain the reaction product. The preferredcom-pound is potassium- Vdi'chromateY since it is. readily soluble, readily available, andn at, the present time onerof the less-expensive sources'of thedes'iredl acidy chromate ion.

The reaction product is thermally stable at an evaporationtemperature of 212 F.

In order to illustrate. the present invention further, reaction products in accordance with the present invention wereiformed by reacting at room temperature twoV primary amines, cyclohexylamine and ani-line, a. secondary'amine,.di-

ethanolamine, a tertiary amine, tri-ethylarnine, and a mixed primary-secondary amine, aminoethylethanolamine, with potassium dichromate in accordance with the procedure set out before. Reaction products were formed which, for convenience in description, will be termed cyclohexylamine chromate, aniline chromate, aminoethylethanolamine chromate, diethanolamine chromate and tri-ethylamine chromate, but Vit is to be clearly understood that I do not wish to limit myself by such terminology since the exact structural composition of the reaction product is not understood.

The reaction products of the several amines and potassium dichromate were then added to oxygen saturated surface water (from the San Jacinto River, Harris County, Texas) in varying amounts in a laboratory scale circulating water system in which the Velocity and temperature of the water simulated those of a normal plant cooling system actually employing this river water. Weighed specimens of carbon steel were exposed in this system at two diierent velocities (0.124 and 1.575 feet per second) of this water into which air was continuously bubbled. The difference in corrosion rate of these speciments under the influence of the Various inhibitors was determined by conventional laboratory techniques.

These results are compared in Table I which presents the amount of the various inhibitors added to the oxygen bearing water, the corrosion rate and penetration in inches per year as evidenced by the weight loss of the specimens of carbon steel after contact with the corrosive solution and the per cent of reduction.

The data in the foregoing table have been plotted in the single figure of the drawingto illustrate moreA clearly the advantages of the present invention over that of the prior art. From the data presented it is obvious that as little as parts per million of the cyclohexyl amine chromate is as effective an inhibitor as almost'BOO parts per million of potassium dichromate or between 500 and 600 parts per million of cyclohexyl amine. This is particularly significantl since it is known that introduction of too low a concentration of an inhibitor such as potassium chromate will actually increase the corrosion as shown by U. R. Evans in, his article Use of soluble inhibitors, fundamental principles, Industrial and Engineering Chemistry, 37:703, 1945. i Y. r

- The v,data further illustrateythat the tertiary amine, triethyl, amine, when reacted with potassium ydichromate has this same synergistic inhibiting eiect because a Accncentraticn of about 10 partsper million of this reaction prod-uct is as eiectiveas about 300parts per million of chromate or 600 to 700 parts pei` million of the amine. Calculation of the concentrationof a mixture of either of` these amines and potassium chromate that must be used to give at least as good inhibition as eitherone alone, would indicate the use of a total concentration not significantly lower than that of either compound in its purest state. For-example, tov reduce the penetration to 0.03 inch per year, the data presented, which are plotted in the drawing, would indicate the necessity of using a concentration of about 200 parts per millionof potassium chromate or about 250 parts per million of triethylamine, or possiblya mixture of about 100 parts per million of potassium chromate and about 125 parts per million of triethylamine. Instead of this, a concentration of less than 10 parts per million of the reaction product prepared in accordance with the` present invention may be used. Thus, the unexpected inhibiting properties of this reaction product allow-much lower concentrations of inhibitor to be used with the same or superior effects to that obtained with much higher concentrations. off potassium chromate or amine alone.; A comparison of the inhibiting properties of several of the amine chromates prepared in accordance with this invention with that of potassium chromate under the same conditions is also given in the drawing.

Water was then saturated with carbon dioxide at atmospheric pressure and room temperature of 85 F. The pH of the saturated solution was 5.2. Portions of the Water were then tested for corrosity to specimens of carbon steel, while other portions had added to it potassium chromate, cyclohexylamine and the reaction product of cyclohexylamine and potassium di-chromate in Varying quantities using the circulating system previously described. The specimens of carbon steel Y were exposed to the corrosive action of the solution of carbon dioxide for identical lengths of time, withdrawn and weighed to determine the metal loss. The following table gives the concentration of the inhibitor in the carbon dioxide solution, the corrosion rate measured in penetration of the metal in inches per year and the per cent of reduction as shown by the several inhibitors. y

TABLE II Corrosion of carbon steel by wetter saturated with carbon dioxide 1 1 Saturated with carbon dioxide at atmospheric pressure and room temperature F.). pH of saturated solution is 5.2.

It will be immediately apparent from the foregoing data thatV 100, 500 and 1000 p. p. 1n. of potassium chromate added to the corrosivesolution of carbon dioxide` resulted in reduction of TABLE V l0 reaction product of the amine and the salt with the ferrous metal surface. The characteristics and behavior of ferrous metals treated in accordance With the present invention in which they are contacted with an aqueous solution containing oxygen or carbon dioxide to Which has been added Corrosion,` of carbon steel by acid solutions Solution Inhibitor Added HC1 Solution l 5,000 D. D. ID. K2Cl201 5,000 Pyridine Chromate None 5,000 p. p, m. Pyridine None 1,000 p. p. m. Cyelohexylamine Chromate.

Corrosion Percent rate, in./ Reducyr tion 1 Static solution in a beaker at room temperature (85 FJ. 2 Increased.

It will be seen from the data in Table V that both potassium dichromate and the reaction product of potassium dichromate and pyridine actually increased the corrosivity of hydrochloric acid to the specimens of carbon steel, while some reduction in corrosion was obtained with pyridine. Similarly, it may be seen that the potassium dichromate and the reaction product thereof with pyridine all increased the corrosivity of the 40% sulfuric acid solution to carbon steel, While the reaction product of cyclohexylamine and potassium dichromate in an amount of 1000 p. p. m. reduced the corrosivity of 10% acetic acid solution to carbon steel by 46.3

The present invention is susceptible to application to inhibition of any type of ferrous metal surfaces in contact with a corrosive solution containing oxygen, hydrogen sulde or carbon dioxide. For example, in many industrial plants, including petroleum refineries, it is frequently necessary to use Water in contact with various metallic equipment such as condensers, condenser boxes, heat exchangers and the like. Since this Water contains oxygen, it is frequently very corrosive, resulting in loss to both equipment and operating eciency.

The invention is also applicable to the storage and transportation of petroleum and its products, since entrained Water settles out in pipe lines and tanks and this Water containing oxygen, carbon dioxide, and/or hydrogen sulfide is usually the cause of corrosion of pipe lines with the attendant economic loss requiring shutdown of equipment and replacement thereof. It is, therefore, considered that the present invention has Wide application to any operation in which ferrous metal alloys are exposed to the corrosive action of aqueous solutions containing oxygen, hydrogen sulfide and/0r carbon dioxide.

The invention may also be applicable to the prevention of corrosion of steel tubing, Well head equipment, and product lines experienced in some gas condensate Wells producing sweet gas or condensate uids by contact With connate Water or entrained Water which contains carbon dioxide and organic acids as the corrosive media.

The mechanism by which the reaction product of an acid chromium salt and an amine is effective in preventing corrosion of ferrous metals is not fully understood, but it is believed that the protection is based on an extremely thin, selfhealing lm formed by the interaction of the the reaction product of an `amine and acid chromium salt bears a striking resemblance to the resistance of the ferrous alloy stainless steel to corrosion. It is believed that the activity of the iron surface may be passivated by the reaction product of the amine and the acid salt. In other Words, the iron becomes more noble than prior to treatment and less `susceptible to attack because the positive electrochemical potential of the iron surface is reduced. It is understood, of course, that I do not Wish to bind myself to any theory offered as explanation of the benecial effects of this invention.

While numerous examples of amines have been given, it is to be understood that I do not Wish to limit myself thereto and that any primary, secondary, or tertiary amine may be used in reaction With any compound selected from the group of chromic acids, salts of polychromic acids, or acid chromium salts. Examples of some other primary amines that may be used With the present invention are butylamine, methylamine, propylamine, benzylamine, ethanolamine, and isoamylamine. Other secondary amines that may be used with the present invention are dibutylamine, dimethylamine, diphenylamine, methylethanolamine, dimethanolamine, and dipropylamine. Additional tertiary amines that may be used with the present invention are tributylamine, trimethylamine, triethanolamine, methyldi-ethylamine, and tripropylamine. Complex or mixed amines may also be used with the present invention. Some examples of these other than the aminoethylethanolamine used herein are melamine, diazine, and triazine (either the symmetrical or unsymrnetrical isomers).

Also it is to be understood that while I have confined my description and examples to the alkali metal dichromates, such as illustrated by potassium dichromate, the other alkali metal dichromates such as the lithium and sodium dichromates may be used in lieu thereof although the potassium di-chromate forms a preferred reactant in the practice of my invention. It is also to be understood that While potassium dichromate has been employed as an illustration thereof, other salts may be used, such as for example lithium and sodium dichromates and other chromium salts may be used in lieu of potassium dichromate.

The nature and objects of the present invention having been fully described and illustrated, what I wish: to. claim. as new'. .and-:useful.and-to.T secure.. by. LettersPatentis: Y

1. LA methodrfor. inhibitingfhe. .corrosivitysoi aqueous .v solutions containing corrosive amounts` cffaJ corrosive 'materialselected -from thefclass` consisting. of oxygen, .hydrogen sulde,` carbon. dioxide, and their mixtures in contact With a ferrous metal surface which comprises adding to said corrosive solution a small but effective amount of the reaction product resulting when an only partially saturated aqueous, solution of an acidic chromium salt havinga :pHlessl-than 7 has added theretoan amine selected from the group consisting of primary, secondary',"tertiary and mixed amines at a temperature Within the range of 60 to 100 F., the amine and the solution of acidic chromium salt being employed: in-

amounts sufficient to provide equimolar amountsY of amine and acidic chromiumef'salt to;iorm ahomogeneous solution of said reaction' product',

2. A method for inhibiting the corrosivityfof* aqueous solutions containing corrosive-'amounts''V of a corrosive material selected from the class consisting of oxygen, hydrogen sulfide, carbon dioxide, .and their mixtures acontact. vvitha` ferrous metal surfacewhich .comprises adding. ,to-

said corrosivesolution prior. tocontact withsaid..

ferrous metal surface an amount of the reactionv product resultingvwhen an. only`....partiallyl.satua1 rated aqueous solution consisting of., an acidic chromiu'msalt having a pHlessth'anIZ has added 60 to `v100-""1.', the amine and .the solutio'nois acidiclchromium saltbeingfemployedin amounts sufficient Vto .provideequmolaramounts of amine andv acidic chromium saltto form a homogeneous solution of. said reactionproduct inthe range from 5 to 500 parts permillion of said corrosive solution.

3. A method for inhibiting the ccrrosivity of aqueous solutions containing corrosive amounts of a corrosive material selected from the class consisting of..oxygen,.,hydrogen sulde, carbon dioxide, and their mixtures in contact with a ferrous metal surface which comprises adding to saidcorrosive solution an amount ofthe reaction product resulting when an only partially saturated aqueous solution of' potassiumdichromate' has added theretovan-'amine selected from the group Aconsisting .ofz primary, secondary, tertiary and mixed amines; at-a. :temperature within the range of` 60 'to 1009MB; the amineand the solu-I tion of. potassium-'dichromate being employed `in amounts suicientto provide equimolar amounts of-'amine and-potassium dichromate to-form a homogeneous -solution Vof Y'saidY reaction product in the range between 5 and-500 parts per million of said corrosive solution.

PRENTISS S. VILES.

REFERENCES CITEDl The following references are of record Ain the iile of this patent:

UNITED STATES :PATENTS Number Name Date 2,294,525 Waugh Sept. 1, 1942 2,478,755 Elder Aug. 9, 1949 2,478,756 Elder Aug. 9, 1949 2,480,754 McCarthy Aug,30`, 1949 

1. A METHOD FOR INHIBITING THE CORROSIVITY OF AQUEOUS SOLUTIONS CONTAINING CORROSIVE AMOUNTS OF A CORROSIVE MATERIAL SELECTED FROM THE CLASS CONSISTING OF OXYGEN, HYDROGEN SULFIDE, CARBON DIOXIDE, AND THEIR MIXTURES IN CONTACT WITH A FERROUS METAL SURFACE WHICH COMPRISES ADDING TO SAID CORROSIVE SOLUTION A SMALL BUT EFFECTIVE AMOUNT OF THE REACTION PRODUCT RESULTING WHEN AN ONLY PARTIALLY SATURATED AQUEOUS SOLUTION TO AN ACIDIC CHROMIUM SALT HAVING A PH LESS THAN 7 HAS ADDED THERETO AN AMINE SELECTED FROM THE GROUP CONSISTING OF PRIMARY, SECONDARY, TERTIARY AND MIXED AMINES AT A TEMPERATURE WITHIN THE RANGE OF 60* TO 100* F., THE AMINE AND THE SOLUTION OF ACIDIC CHROMIUM SALT BEING EMPLOYED IN AMOUNTS SUFFICIENT TO PROVIDE EQUIMOLAR AMOUNTS OF AMINE AND ACIDIC CHROMIUM SALT TO FORM A HOMOGENEOUS SOLUTION OF SAID REACTION PRODUCT. 